1. Field of the Invention
The present invention relates to an exhaust heat recovery apparatus that recovers the exhaust heat from a heat engine.
2. Description of the Related Art
An exhaust heat recovery apparatus is available that, using a heat engine, recovers the exhaust heat from an internal combustion engine that is mounted on a vehicle, such as a passenger car, a bus and a truck. With regard to the exhaust heat recovery apparatus used for such a purpose, external combustion engines, such as the Stirling engine, which is excellent in theoretical thermal efficiency, are used, for example. Japanese Patent Application Publication No. 2003-518458 (JP-A-2003-518458) discloses a technology in which a clutch is provided between the internal combustion engine and the Stirling engine.
In an external combustion engine, such as the Stirling engine, the heat input from a heat source, such as the exhaust gas, is transferred to a working fluid of the external combustion engine through a heat exchanger. Accordingly, an external combustion engine is less responsive to the variation of heat input, and the output therefrom is slow in following a rapid variation of heat input. In addition, because an exhaust heat recovery system uses a low-quality heat source, such as the exhaust gas from a heat engine, the obtained power output is low relative to the size of the exhaust heat recovery system. As a result, in a case where the rotation speed of the heat engine rapidly increases because rapid acceleration is required, for example, if it is attempted to increase the rotation speed of the exhaust heat recovery means with the rotation speed of the heat engine, it may be impossible to obtain the sufficient motive power to increase the rotation speed of the exhaust heat recovery means through exhaust heat recovery. Thus, in the configuration in which the motive power from the exhaust heat recovery means and the motive power from the heat engine are output, it is possible that the heat engine drives the exhaust heat recovery means, and that the motive power from the heat engine is used by the exhaust heat recovery means. As a result, the power output from the heat engine can be reduced, and it is possible that required acceleration cannot be obtained.
In JP-A-2003-518458, there is no mention of the above problem concerning the configuration in which the motive power from the exhaust heat recovery means and the motive power from the heat engine are output, and there is yet room for improvement.